This invention is concerned with improvements in or relating to fluid pressure actuated presses.
In carrying out many different kinds of pressing operation, it is necessary to maintain platens of the press substantially parallel to one another. For example, when a press is used to cut a workpiece by pressing a cutting edge of a die through the workpiece, it is necessary for the platens to be substantially parallel if complete penetration of the workpiece is to be achieved.
In United Kingdom Pat. No. 1,035,816, there is described a press in which an upper platen is moved by two piston and cylinder assemblies and is maintained parallel to a lower platen of the press by valve balancing means. The valve balancing means operates, in response to an advance of a portion of the upper platen connected to one of the assemblies relative to a portion of the upper platen connected to the other assembly, to reduce the supply of hydraulic fluid to the assembly connected to the advanced portion by bleeding the hydraulic fluid to a collecting tank so that the operation of that assembly is slowed and a compensating advance of the other portion of the upper platen is caused to occur. However, this arrangement is wasteful in that much hydraulic fluid may be pumped straight to the tank without being used in a pressing operation with a consequent waste of the energy used to pump this fluid.